EDI Repeated Segments
In EDI there is a construct called a Loop. But this is not like you think of a loop using an while statement. EDI is a file format, not a programming language. When we speak of Loops in EDI, what we are really talking about is repeated structures, or segments.
EDI is not a flat file, but it does have repeated lines or segments. Some times this repetition comes in groups and sometimes its just a line that get repeated in part of the document. Repeating structured data is fundamental to EDI, but can become difficult to interpret at times. Understanding the types of repeating structures and when and where they may occur can save a lot of time.
Repetition
There are three kinds of loops/repeated segments; First there is a simple segment that can appear more than once. Lets call this a Repeating Segment. Second there is a group of segments that appear together, and may repeat. Lets call this a Repeating Group. And finally there is a segment or group that repeats within a beginning and ending loop envelope. Lets call this a Repeating Envelop.
Repeating Segments
A repeating segment is pretty much just what it sounds like, a segment that may occur more than one time. A good example of this would be the AMT segment. The AMT is a segment that contains a monetary value. The AMT_01 declares what type of value it is, and the AMT_02 has the amount of money. In an EDI document like an invoice, we may need to have many values, subtotals, taxes, base price, and so on. Having a repeating segment lets us put all of these values on their own independent segment to be interpreted and included as best fits the Trading Partners and the nature of the transaction.
Here is an example of an unwrapped N1 group where the N3 is repeated:
N1*AC*ARTHUR JONES*1*9012345918341*11*SE~
N2*GEORGE WASHINGTON~
N3*157 WEST 57TH STREET~
N3*Suite 2001*5th Floor~
N4*CINCINNATI*OH*43017~
When segments are repeatable, they are indicated with a “Max Use” value of greater than one in the standards and usage specification. In the N1 Group, the N2 and N3 segments may have a max use of 2.
Repeating Groups
A repeating group is also what it sounds like. It is a group of segments that work together and get repeated. This loop is generally referred to by the primary segment. This segment is required in this group. This means that if this group occurs, this segment must also occur.
Most Repeating Groups are contextual. This means that they are defined by the segments that surround them, and are terminated by the first segment that is not in the group, or starting the group again. So a Repeating Group may repeat, but as soon as we move out of the segments in this group, we are done repeating it and move on to the next segments or groups defined in the standard.
The N1 is a good example. The N1 group contains name, address and contact related information. The only required segment is the N1. Subordinate to the N1 (that contains name and such) is the N2 (that contains secondary name or attention type data.) Then comes the N3 (with the street address) and then the N4 (with the city, state, country, zip).
Not all groups have the same letters, like ‘N’ and the N1 group is no different. It also contains the PER segment that contains a persons name, and contact info like phone number or email. Any PER that happens under an N1 is for that location.
In a document like an order you may want to have the address and contact for the shipper, the receiver, a biller, and a payer. There are many possibilities, and these are all repeated in this group. Here is an example of an unwrapped N1 group where the that is repeated:
N1*ST*MRS JONES*1*123456789*11*SE~
N2*BEVERLY SIMPSON~
N3*157 WEST 57TH STREET~
N4*CINCINNATI*OH*43017~
N1*SF*MR JONES*1*9012345918341*11*SE~
N2*MAGGIE MCGILLICUTTY~
N3*1001 MAPLE STREET~
N4*PITTSBURGH*PA*86753~
Segments that are in a repeating group are listed as being in a Loop. They may be repeated whenever the loop is repeated as specified in the standards and usage specification. Thus you may have a max use of the N3 as 2, and an N1 Loop that has a max use of 1000. So really you could see 2000 N3 segments, (2 for each of the 1000 possible N1 loops).
Repeating Envelope
A repeating envelope makes reference to EDI Enveloping. Basically, the ISA-IEA envelope can contain one or more GS-GE envelopes. And each GS-GE can contain more than one ST-SE envelope. These levels of enveloping are covered in greater detail on the EDI Enveloping page. But it doesn’t have to stop there. In the 3050 850 document there is a loop called LS-LE that contains terms. This section happens inside the ST-SE. And there is nothing to prevent other sub envelops from happening where there is a need.
What is fundamental to these types of loops is that they have a designated beginning, and ending. They must have both. Repeating Groups end when a beginning of a new iteration of the loop is found, or a segment that is not in the group is found. This can leave some ambiguity if the standard is not followed closely. The Repeating Envelope leaves nothing to chance and declares that it is done.
A note about Required segments
You may have noticed in the examples above or in the specification that we referenced that there are required segments in loops that are optional. This is not a contradiction and I will explain this here. A loop may be optional. If it is, then it may be ommitted entirely from a document while still compliant with the standard. If the loop is included, then the required and optional segments within that loop apply. And they apply in each instance of the loop. (We can’t have an second N1 loop unless we include the required N1 segment.)
Basically this is like scope in XML. The requirements of mandatory or optional only apply within the scope of the loop where they are defines. in the same fashion as sub nodes in and XML hierarchy.
Basic Fundamentals to Remember
- Some segments can occur more than once, or can be repeated.
- Some groups of segments can and often do occur more than once. These are contextual and are terminated by segments after the group in the standard.
- Some segments are encapsulated in beginning and ending segments like enveloping. These segments can repeat, but only in another encapsulation or envelope.
- The standard will indicate when repetition is allowed.
–
Looking for something else relating to EDI? Check out the EDI Primer post
–
Subscribe to "The Integration Engineer" by Email
Find out about the tools and services available at The Integration Engineer's Consulting site.
